In coronary artery disease, the build-up of artherosclerotic plaque on the inner walls of the coronary arteries causes a narrowing or complete closure of these arteries, resulting in insufficient blood flow to the heart. This condition has become one of the most common life-threatening medical problems facing older men and women.
A number of approaches have been developed for treating coronary artery disease. In less severe cases, it is often sufficient to treat the symptoms with pharmaceuticals and lifestyle modification to lessen the underlying causes of the disease. In more severe cases, a coronary artery blockage can often be treated using endovascular techniques such as balloon angioplasty, atherectomy, laser or hot tip ablation, placement of stents, and the like.
In cases where pharmaceutical treatment and/or endovascular approaches have failed or am likely to fail, it is often necessary to perform a coronary artery bypass graft procedure using open surgical methods. Such methods require that the patient's sternum be divided longitudinally and the chest be spread apart to provide access to the heart, an access technique known as a median sternotomy. While the patient's heart is arrested using cardioplegic agents and the patient is supported by cardiopulmonary bypass, a vascular source of arterial blood is then connected to a coronary artery downstream from the blockage. The arterial blood source may be a venous or arterial graft vessel connected between an arterial source such as the aorta and the coronary artery. Another common arterial blood source is the left or right internal mammary artery which may be grafted to the coronary artery which is narrowed or occluded. Recent studies have suggested that the use of mammary arteries as an arterial blood source may be advantageous over other sources due to a greater likelihood that the graft will remain patent over time.
In order to use a mammary arterial graft in a coronary artery bypass procedure, blood flow through the target mammary artery must be temporarily stopped. For this purpose, a removable surgical clamp is applied to the mammary artery at a position downstream from the patient's aorta. In a conventional open-chest procedure, a relatively large, easy to handle clamp is used which can be applied by hand or with a forcep directly to the mammary artery through the large opening in the patient's chest provided by a median sternotomy. After the mammary artery is clamped, it is ligated and divided at a location downstream from the clamp to create a free end which may be connected to the coronary artery. After the grafting is complete, the clamp is removed by the surgeon, again typically by hand or with the open forceps, to permit blood to flow through the mammary artery and into the coronary artery downstream of the blockage.
While very effective in many cases, conventional open heart surgical techniques of coronary artery bypass grafting are highly traumatic to the patient due to the necessity of a median sternotomy or other form of gross thoracotomy. Therefore, new methods of performing surgery on the heart using minimally-invasive techniques have been recently developed. In these methods, the patient's heart is arrested by occluding the patient's aorta between the coronary arteries and the brachiocephalic artery with an expandable balloon on the distal end of an endovascular catheter introduced via a femoral artery. Cardioplegic fluid is then delivered to the patient's myocardium through a lumen in the same catheter or through a separate catheter positioned in the coronary sinus. This method allows the surgeon to perform operations such as coronary artery bypass grafting without creating a large opening in the patient's chest. Minimally-invasive cutting and suturing instruments can be introduced thoracoscopically to isolate and dissect a mammary artery and to connect the free end of the mammary artery to an incision in the coronary artery. A complete description of such methods is found in commonly assigned, co-pending application Ser. No. 08/023,778, filed Feb. 22, 1993 now U.S. Pat. No. 5,456,733 which has been incorporated herein by reference.
This new generation of thoracoscopic methods of performing coronary artery bypass grafting has, of course, created many new challenges. One such challenge arises from the inability to clamp the mammary artery by manually applying a surgical clamp through the large opening in the patient's chest. Instead, the clamp must be introduced in a minimally-invasive manner through a small percutaneous incision or cannula positioned in an intercostal space in the patient's rib cage.
It is known in certain surgical procedures, especially laparoscopic procedures, to use long-handled introducers for applying clamps to internal tissue within a body cavity such as the abdomen. These introducers typically include a pair of movable jaws or arms for holding a clamp at the distal end of an elongated shaft. The clamp is placed in the arms of the introducer and the distal end of the introducer is introduced through a trocar sleeve into the body cavity. The clamp is then positioned at the desired tissue location and an actuator on the proximal end of the introducer is actuated to apply the clamp to the tissue. Examples of such systems are seen in U.S. Pat. No. 4,174,715 to Hasson, PCT Application No. PCT/US93/02670 to Gourlay (Publication No. WO 93/18712) and PCT Application No. PCT/US92/06186 to Kensey (Publication No. WO 93/09721).
These known devices, however, suffer from a number of disadvantages. Known introducers typically hold onto the clamp with the same mechanism (e.g. a pair of arms) that allows the clamp to close onto the tissue. Therefore, the jaws of the clamp cannot be allowed to close onto the tissue without releasing the clamp from the arms of the introducer. After the clamp has been applied (and thus released from the introducer), the surgeon cannot manipulate the clamp and the tissue to which it is attached by manipulating the introducer. In addition, it may be necessary to reapply the clamp if the first attempt did not completely occlude the blood vessel or if the clamp was improperly positioned. Thus, the surgeon must relocate the clamp and engage it with the introducer to open the jaws and reposition the clamp. This is particularly difficult in minimally invasive procedures in which visualization and access is limited.
Another disadvantage of known introducers is that the clamp is typically held by the introducer at multiple engagement points. For example, the device disclosed in the Gourlay application closes two arms on the distal end of the introducer onto two handles on the proximal end of the clamp to grasp the clamp. This approach makes it very difficult to re-engage the clamp because the surgeon must line up the arms of the introducer with both handles of the clamp. This further limits the angle in which the clamp may be approached and re-engaged by the introducer arms.
Further, known clamps and introducers are not well-suited for occluding a mammary artery in coronary artery bypass grafting procedures. For example, blood flows through the mammary artery at a higher pressure (typically 70-100 mm of mercury) than the pressure in other fluid conducting ducts to which such clamps are typically applied. Known clamps that can be introduced through a percutaneous incision in the body generally do not provide sufficient clamping force to occlude the mammary artery. Moreover, the clamps and forceps used for arterial clamping in open-chest surgery are typically adapted for manual insertion through a gross thoracotomy and are usually too large to be introduced through a small percutaneous, intercostal incision or cannula.
For these and other reasons, improved systems and methods are desired for clamping fluid-carrying vessels in a body cavity via a small percutaneous incision or cannula. Preferably, the system would be capable of temporarily occluding a mammary artery during a coronary artery bypass grafting procedure. The system should allow the surgeon to apply the clamp onto the mammary artery without releasing the clamp from the introducer so that the clamp may be repositioned without having to relocate the clamp. The system should also allow the clamp to be engaged and opened at a single point. In addition, the system should be configured for delivery through a percutaneous intercostal incision and the clamp should have sufficient closing force to completely occlude the mammary artery without damaging the vessel under blood flow pressures of 100 mm Hg or greater.